This invention relates to techniques for irradiating materials with an electron beam, and more particularly relates to techniques for selectively controlling the delivery of electron beam radiation to a material being processed.
Electron beam (E-beam) irradiation techniques are employed in an increasingly wide range of manufacturing and processing applications, including, for example, medical, consumer, automotive, military, and aerospace applications. For many production applications, E-beam irradiation techniques are superior alternatives to conventional thermal-based processing for accomplishing various manufacturing steps. Such is the case for, e.g., E-beam welding, as well as for the class of E-beam curing applications including E-beam polymerization of composites and E-beam polymerization of bonding adhesives.
In a typical E-beam welding operation, the junction between two abutting metal parts to be welded together is exposed to a beam of electrons to melt the junction and fuse the parts together upon cooling. E-beam polymerization, i.e., curing, operations typically involve the exposure of a radiation-curable polymer-based material to a beam of electrons to cross-link the polymer and thereby cure the material. This radiation curing process can be employed, for example, for curing a structural part formed of a radiation-sensitive, fiber-reinforced polymer matrix composite. The radiation curing process can also be employed, for example, in a bonding operation in which a radiation-curable polymer adhesive that is applied to junctions of a structural assembly is exposed to a beam of electrons to cure the adhesive and thereby bond together the components of the assembly.
E-beam curing processes such as these provide substantial cost and efficiency advantages, particularly in a production environment, and notably because the E-beam curing of a polymer matrix composite or polymer adhesive can be accomplished in a time that is typically greatly reduced from that required for conventional thermal curing. In addition, because E-beam curing can be accomplished at room temperature, it enables high manufacturing throughput, reduced residual stress in processed materials, accommodation of material assemblies that include temperature-sensitive materials such as plastics, and elimination of volatile organic by-product release during the cure. Furthermore, because an E-beam can penetrate many materials, complicated multi-material assemblies can be bonded in an E-beam process where the assembly adhesive is not exposed and the E-beam is directed through the assembly to an internal location of E-beam sensitive material to be cured.
For many E-beam curing applications, it is preferable to irradiate only selected portions of a material or an assembly. For example, in a bonding application, irradiation is generally required only along the adhesive bond lines of the assembly, and typically the bond lines are of an area that is only a small fraction of the total surface area of the assembly; irradiation of the entire assembly is thus unnecessary. The inefficiency of E-beam radiation of the entire assembly area reduces process throughput and increases process cost. In a polymer matrix curing application, multiple polymer resins may be employed in the same part or assembly of parts, with each resin possibly requiring a distinct E-beam polymerization dose. A uniform irradiation of all resins could result in damage or inoperability of the part or assembly. It is clear that for these example E-beam applications as well as other various applications, blanket irradiation of a part or assembly often produces only suboptimal process products and substantially reduces process efficiency.